The present invention relates to an automatic drawn arc welding apparatus for securing nuts to metal surfaces and, more particularly, to an air feed weld gun with retractable piston that has a dual piston mechanism for supplying welding gasses and/or air to the nut hole during the welding operation.
Traditionally, weld nut guns have a collet. The spring forces in a slit collet hold a weld nut during the welding operation. Often, weld spatter from the welding process coats the threads on a weld nut, leading to significant cost and time loses due to component rework.
To date, automatic feed weld guns which provide a supply of welding gasses to the threads of the nut during the welding process have proven relatively successful. As shown in FIG. 1, these prior weld guns 15 utilized a primary piston assembly 16 which is driven within a cylindrical working chamber 17. The primary piston assembly 16 drives a hollow first driven piston 18. The prior art weld gun 16 utilizes several sealable passages 19 to provide welding gasses through the hollow first driven piston. To effectuate sealing off of the through passages 19, the primary piston assembly 16 utilizes a second fixed piston 20 disposed through the primary piston assembly 16. Disposed between the primary piston assembly 16 and the fixed piston 20 is a series of seals 21. Over time, these seals 21 have the tendency to leak, thus allowing compressed welding gasses from the air supply 22 to enter the back portion 23 of the working chamber 17. This inhibits the ability of the primary piston assembly 16 to return to its fully retracted position within the cylindrical working cavity 17.
A need, therefore, exists for an apparatus and system which can automatically feed a weld fastener such as a nut or a stud to a welding surface. The apparatus provides welding gasses to the threaded portion of the weld nut to minimize the chance that weld spatter material will be incorporated into the threads. A need further exists for an automatic feed weld gun with an improved return feature which is resistant to degradation caused by cycling of the weld gun.
In one preferred embodiment, a blow feed weld gun for welding a nut to a metal substrate is disclosed. The blow feed weld gun has an air feed mechanism and a primary piston assembly. The primary piston assembly contains a primary piston assembly located within a cylindrical working chamber. The primary piston assembly is coupled to a first driven piston which is hollow and defines a passage which welding gasses can be delivered to the threads of a weld nut. Slidably disposed adjacent the first driven piston is a second interior piston. A second interior piston, which is coupled to the primary piston assembly, regulates gasses through an axial bore of the first driven piston.
In yet another preferred embodiment, the second interior piston is disposed within the passage of the first driven piston. Movement of the second interior piston is regulated by a pin which engages a slot formed within the first driven piston.
In yet another preferred embodiment, the regulating pin of the second interior piston engages a forward wall of the cylindrical working chamber to affect the timing of release of welding gasses into the passage of the first driven piston.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.